Field of the Invention
The present invention relates to a diagnostic device and a diagnostic method for a motor unit of an electric vehicle, and relates to a self-diagnosis function of an oil supply system that supplies an oil used for lubricating a reduction gear unit or cooling the motor unit.
Description of Related Art
An electric vehicle may experience a malfunction of a motor unit for driving the vehicle or a malfunction of a controller that controls the motor unit. This can significantly affect the travel performance or travel safety. In particular, in the case where an in-wheel motor drive apparatus is used in an electric vehicle, rapid rotation of a wheel bearing unit, a reduction gear unit, and a motor unit, which are components of the apparatus, is involved as a result of size reduction of the apparatus. Thus, reliability of these components is an urgent concern for the in-wheel motor drive apparatus. Hitherto, an in-wheel motor drive apparatus has been proposed in which, in order to ensure the reliability, during traveling of a vehicle, the temperature of components such as a wheel bearing unit, a reduction gear unit, and a motor unit is measured and monitored for overload with features to limit a drive current in the motor unit or to reduce a rotational frequency of the motor unit according to the temperature measurements (e.g., see the Patent Document 1 listed below).    [Prior Art Literature]
[Patent Document 1] JP Laid-open Patent Publication No. 2008-168790
In an in-wheel motor type electric vehicle, a motor unit having high responsibility is independently mounted to each wheel. In particular, in the case where drive torque of each motor unit which is a drive source of the electric vehicle is transmitted to the corresponding wheel via a reduction gear unit having a high reduction gear ratio, torque of each motor unit caused by destabilization of motor control is increased and transmitted to the corresponding wheel. Thus, at a time of a malfunction of the motor unit or the reduction gear unit, it is necessary to take measures corresponding to the situation in order to keep a stable vehicle attitude.
In each motor unit, a rotor and a stator are cooled directly by an oil, and the reduction gear unit is lubricated and cooled by this oil. In order to prevent a malfunction of the reduction gear unit, it has been necessary to grasp the contamination state, the degradation state, or the amount of the oil and to issue a warning when it is out of a specified value, thereby prompting maintenance of the vehicle. However, air is mixed into the oil during rotation of the reduction gear unit, and thus it is difficult to measure the degradation state or the like of the oil.
As described above, in the in-wheel motor drive apparatus, during traveling of the vehicle, the temperature of the motor unit is measured and monitored for overload, and driving of the motor unit is restricted. In this case as well, during traveling of the vehicle, the reduction gear unit rotates, the oil bubbles, and air is mixed into the oil. Thus, it is difficult to measure the degradation state or the like of the oil.